Method of generating alternating currents.



PATENTED JUNE 9, 1908. A. D. LUNT. METHOD OF GENERATING ALTERNATING GURRENTS.

APPLIOATION I'ILED AUG. 25, 1899.

H0 MODEL.

INVENTIJ .741 exander D, Lwnt y 4M Z M WITNESSES.

No. 730,673, rammed June 9, 1903.

UNITED STATES PATENT OFFICE.

ALEXANDER D. LUNT, OF SCHENECTADY, NEW YORK, ASSIGNORTO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

METHOD OF'GENERATING ALTERNATING CURRENTS.

SPECIFICATION forming part of Letters Patent No. 730,673, dated. June 9, 1903. Application filed August 25, 1899. Serial No. 728,411. (No model- To whom it y 6071166771! type. The windings of the fieldmagnet Be it known that I, ALEXANDER D. LUNT, structure 3 are connected with the singlea citizen of the United States, residing at phase conductors 1 2 by means of suitable Schenectady, county of Schenectady, State of leads 4 5, as shown. Within the influence of 5 New York, have invented certain new and the field are two rotating armatures, one of useful Improvements in Methods of Generatwhich is of the squirrel-cage type and is shown ing Alternating Currents, of which the folat 6, while the other is provided with a defilowing is a specification. nite winding and is indicated at 7. Both ar- I-Ieretofore in cases where single-phase almatures have the sameaxis of rotation, and

10 ternating currents are changed into or are one of the a'rmatures is placed between the produced from other alternating currents difother armature and the field-magnet strucfering in phase or frequency, or both, the curture 3. In the construction shown the squirrent or currents resulting from the change rel-cage armature 6 is arranged so as to surare composed of a fundamental wave and a round the definitely-wound armature 7.

I5 wave or waves of higher frequency of such The last-mentioned armature has its windnature as to render the resultant wave of iring tapped at suitable points and connected regular frequency, varying from period to to collector-rings carried by the armatureperiod. Such currents are unsuitable for shaft. The winding may be tapped so as to many purposesas, for instance, the operaproduce or consume either single-phase cur- 20 tion of synchronous motors,rotary converters, rent or multiphase current, as may be deor other machines which are sensitive to vasired. I have indicated in Fig. 1 the connecriations in frequency of current and by reations corresponding to the single-phase arson of this sensitiveness are set into oscillarangement; but it will be evident that the tion or, in other words, caused to hunt. connections might equally as Well be made 25 My invention aims to do away with the obfor a multiphase current of any number of jections mentioned by producing alternating phases. By Way of example I have indicated current of uniform frequency from another in Fig. 2 the additional connections and colalternating current of uniform frequency, lector-rings to be used in conjunction with either single phase or multiphase. the armature 7 in Fig. 1, where it is desired 30 The details of my invention and the mode either to produce or consume two-phase curof putting the same into practice will be betrents. Where I have used the terms proter understood by reference to the following duce and consume or their equivalents description, taken in connection with the acin the above description, I do so with a view companying drawings, while its scope will be to making clearthe fact that the apparatus 3 5 particularly pointed out in the appended described is reversible in function and may claims. be used for altering the character of a sin- Figure 1 represents in diagram. one embodigle phase current, thereby producing anment of my invention, and Fig. 2a modified other current, either of different phase or difdetail. ferent frequency, or both, or for performing 40 In the drawings, 1 and 2 indicate conduca the reverse operation. tors upon which single-phase electromotive In operating the machine P it is necessary forces are maintained. The machine by that the definitely-wound armature 7 be mainwhich the phase or frequency of the altertained in rotation relatively to its field-magnating current is to be changed is indicated net at some predetermined rate, either above 45 at P. This machine is provided with a fieldor below that corresponding to the frequency 5 magnet structure 3, which, although shown of the current supplied to the machine. Any in diagram in the drawings, is, however, of suitable means may be employed for effectany suitable form-as, for example, like that ing this result; but for reasons of economy, employed in connection with ordinary alteras well as convenience, I find it desirable to 50 mating-current motors of the single-phase employ for this purposeasynchronous motor seems supplied with energy from a suitable source. This motorIhave shown in the drawings at M, the armature of the motor being connected with the alternating mains 1 2, while the field is excited from any suitable source of direct current-as, for example, an exciterE. The machine M is to be connected with the machine P, so as to maintain thelattermachine at the speed desired. This result may obviously be secured in many ditferent Ways as, for example, by directly connecting the two machines and making the number of poles of the machine M such as to correspond with the speed desired or by a belt running over pulleys of suitable relative diameters or in other well-known ways. As symbolical of a suitable mechanical connection I have indicated a belt in dotted lines at 8. In the arrangement shown the pulley on the machine P is of smaller diameter than that on the machine M in order to cause the armature 7 to rotate at a speed higher than that corresponding to synchronism. It is to be understood, however, that the speed of the machine 7 is to be chosen according to the results to be accomplished.

Let it be supposed that the field of the ma chine P is excited by single-phase alternating current. Au alternating magnetomotive force is thus set up between the pole-pieces of the machine. If under these circumstances the flux-screen be given an initial rotation, it will accelerate in speed until it closely approximates synchronism, thereby causing the alternating currents set up in the bars of the squirrel-cage to react upon the impressed magnetomotive force, so as to produce a resultant field indistinguishable from the rotary field produced in a multiphase machine. Within this field the armature '7 is caused to rotate at a predetermined relative speed, thereby setting up currents in its windings of afrequency corresponding to the difference between the speeds of rotation of the rotary field and the armature 7. The currents produced in the winding of the armature 7 may be: conducted to a consumption circuit or circuits in the usual manner by the employment of suitable collector-rings, brushes, and cooperating connections in a manner well understood and as indicated diagrammatically in the drawings.

It is to be noted that with a given speed of its armature 7 the machine Pmay be caused to yield currents of either of two frequencies, dependent upon the direction in which the flux-screen 6 is set into rotation. With a fixed direction of rotation of the armature 7 the currents set up in its winding are of a frequency corresponding approximately to the sum of the speeds of rotation of the armature 7 and flux-screen 6 when they rotate in opposite directions and to their difference in speeds when they rotate in the same direction. More accurately speaking, the currents are of a frequency exactly equal to the difference in speed of rotation of the armature 7 and the fieldlin which it rotates. Thus with a given arrangement of apparatus it is possible to produce at will a current of a 'fre- 7o quency higher or lower thanthat supplied to the imachine, depending upon the direction in which the flux-screen is rotated initially.

l he action ofthe devicemay also be explained upon the theory of two oppositely-rotl1e, currents set up in its conductors react 8) unequally upon the magnetomotive forces and cause one of them to be practically suppressed when thefiux-screen is rotating at fulLspeed, thereby producing a uniformlyrotating flux, due to the other magnetomotive'force, within the influence of which fiux' the frequency-changer armature 7 is rotated as described. I

Some additional actions take place in'the operation of the frequency-changer, as illustrated in the drawings. When the armature 7 of the frequency-changer proper is rotated below synchronism, the machine has a positive torque, thus acting to drive the synchronous machine M as a generator and cause energy to be returned to the line. On the other hand, when the frequency-changer is driven above synchronismthat is, in the same direction, but at a higher speed than that of the impressed rotating fie1dthe machine acts as an induction-generator. The synchronous machine M then acts as a motor, and the energy expended by it, neglecting minor losses, is returned to the linethrough the medium of the frequency-changer, due to its action as an induction-generator.

What I claim as new, and desire to secure by Letters Patent of the United States, is

l. The method of changing the frequency of a single-phase alternating current which consists in producing by said current an alternating magnetic field, neutralizing one of the rotary components of said alternating magnetic field and rotating a conductor in the resultant field at a definite speed, thereby inducing therein an alternating electromotive force of a frequency dependent upon the relative motion of the resultant field and said conductor.

2. The method of changing the frequency of a single-phase alternating current which consists in deriving from said current a rotary magnetic field, and rotating a conductor in said rotary field at a definite speed there by inducing in said conductor an alternating current of a frequency dependent upon the relative motion of the rotary field and said conductor.

3. The method which consists in deriving a rotary magnetic field from a single-phase magnetomotive force and rotating a conductor in said magnetic field at a definite speed 4. The method which consists in deriving a rotary magnetic field from a single-phase ICC tive rotation between a conductor and said magnetic field.

7. The method which consists in producing a single-phase magnetomotive force,suppress ing one of the rotary components of said magnetomotive force, and positively rotating a conductor in the resulting field with a frequency bearing a fixed ratio to the frequency of variation of said magnetomotive force.

In witness whereof I have hereunto set my hand this 22d day of August, 1899.

- ALEXANDER D. LUNT.

Witnesses:

BENJAMIN B. HULL, MABEL E. J ACOBSON. 

